Electroelution

Hello,
I have a quick question regarding the principle behind electroelution. I
usually run my polyacrylamide gels using 1x TBE, from which I often cut out
bands and electroelute the fragments.
I have found that when I electroelute using 1x TBE in the dialysis bag and
in the electrphoresis apparatus (in which I place my dialysis bag), the
fragment is out of the gel in 20 minutes at most, at 100 V.
My reasoning has been that having the buffer surrounding buffer the same
concentration as the buffer used to make the gel was necessary in order to
prevent a chemical gradient from forming in addition to the electric one.
My supervisor on the other hand has argued that this is rubbish. He told
me to use 0.5 x TBE in the electroelution apparatus and just TE in the
dialysis bag. Using these instructions though, it takes me over an hour to
get the fragment out, and even then, it does not always look like it is
out.
If someone could explain the theoretical principles behind this procedure,
I would be much obliged. As far as I am concerned, I will stick with what
works for me, but I would like to know why.
--
Regards
Steve
ssanyal at netcom.cahttp://www.geocities.com/SoHo/Lofts/1785